Project Summary/Abstract Alzheimer?s disease, the major cause of dementia, is a fatal neurodegenerative disorder. The primary risk factor for Alzheimer?s disease is age. The prevalence of Alzheimer?s disease increases dramatically when people reach 65 years or older, reaching nearly 50% for people of >85 years old. Therefore, Alzheimer?s disease poses an enormous challenge to the healthcare system, and is a major obstacle for longevity. Extensive scientific research has identified soluble A? aggregates, collectively termed ?oligomers?, as the primary neurotoxins that cause synapse dysfunction and neuronal death. Detailed structural knowledge on these A? oligomers would shed light on the basis of neurotoxicity and facilitate drug development to cure Alzheimer?s disease. Unfortunately, the progress on this front has been painfully slow. In this project, we propose to characterize the structure of A? globulomers formed by the 42-residue isoform of A? protein. Our preliminary studies have shown that, with electron paramagnetic resonance (EPR) spectroscopy, we were able to resolve structural heterogeneity and reveal the antiparallel architecture in A? oligomers. This project will build upon these preliminary studies and further tackle four specific aims. First, we will study the detailed secondary structure of A?42 globulomers using spin label mobility analysis at all 42 residue positions. Second, we will characterize the tertiary structure using intra-molecular distance measurements. Third, we will characterize the quaternary structure through inter-molecular distance analysis. Fourth, we will use protein structure prediction program Rosetta to model the structure of A?42 globulomers and cross-validate the top models using mutagenesis approaches. The field of Alzheimer?s research has suffered from a lack of accurate structural models of A? oligomers. Success in this project will fill this gap and provide unprecedented insights into the structures of A?42 oligomers. The structural knowledge on these oligomers will greatly facilitate the overall effort in understanding and treating Alzheimer?s disease and other amyloid-involved human diseases, including Parkinson?s, Huntington?s, and type 2 diabetes.